This invention relates to a mobile node, a mobile agent and a network system. More particularly, this invention relates to a control method which assists the movement of a node between an IP (Internet Protocol) network capable of executing communication in accordance with both IP version 4 and an IP version 6 and an IP network capable of executing communication in accordance with only the IP version 4 or an IP network capable of executing communication in accordance with only the IP version 6, a mobile agent, and a network system for assisting the movement of the node.
With a drastic development of small and lightweight nodes and the Internet, the demand for taking out a node from an office or a home to utilize it everywhere has been increased. When the node is moved to other network in the conventional network environment making use of the TCP/IP (Transmission Control Protocol/Internet Protocol), however, setting of the IP address, which is the information for primarily identifying the node in the IP network, must be changed so as to match with the foreign or visiting network environment.
Even if this change of setting of the IP address is automatically made by utilizing a DHCP (Dynamic Host Configuration Protocol) described in RFC (Request For Comment) 1541 as one of the methods of distributing automatically the IP addresses, there remains the problem that the network connection that has been established already with other nodes by using the IP addresses used in the network before the movement cannot be maintained in succession.
Therefore, methods of assisting the movement of the node between the networks have been devised. A typical among them is a protocol of the third layer (network layer) of an OSI (Open Systems Interconnection) reference model and this protocol pertains to the IP version 4 (hereinafter called the "IPv4") that has gained a wide application in the Internet and the IP version 6 (hereinafter called the "IPv6") the specification of which has now been stipulated so as to solve the problems of address exhaustion in the IPv4. As to these IPv4 and IPv6, "IP Mobility Support in IPv4") (hereinafter called "Mobile IPv4") described in RFC2002 and "Mobility Support in IPv6") (hereinafter called "Mobile IPv6") described in IETF (Internet Engineering Task Force) draft (the latest version of which is "draft-ietf-mobile-ip-ipv6-02.txt") are examples of the known references.
Incidentally, the term "IPv4" used in this specification designates an IP address having an address length of 32 bits while the term "IPv6" designates an IP address having an address length greater than 32 bits.
By making use of these Mobile IPv4 and Mobile IPv6, a user can execute communication in the same way before the movement of the node even when the node is moved to another network, without the necessity for changing the IP address of the node or cutting off the network connection that has already been established with other node before the movement.
Incidentally, the term "node" used in this specification designates all those devices which have an IP address and execute communication by utilizing the IP, such as a PC (Personal Computer), a WS (Work Station), a router, and so forth.
Generally, it is assumed that the movement from the IPv4 to the IPv6 is effected gradually and all the networks do not utilize at once the IPv6. In the mean time, therefore, there exist a network (hereinafter called the "IPv4 network") comprising only those nodes which execute communication by utilizing only the IPv4 (hereinafter called the "IPv4 nodes"), a network (hereinafter called the "IPv6 network") comprising only those nodes which execute communication by utilizing only the IPv6 (hereinafter called the "IPv6 node") and a network (hereinafter called the "IPv4/v6 network") comprising those nodes which execute communication by utilizing both of IPv4 and IPv6 in mixture (hereinafter called the "IPv4/v6 node"), the IPv4 nodes and the Ipv6 nodes.
To beginning with, let's consider the case where the IPv4/v6 network is the one that supports both of Mobile IPv4 and Mobile IPv6. In the Mobile IPv4, messages are exchanged between a mobile node moving between the networks and a mobile agent (hereinafter called the "IPv4 mobile agent") for assisting the movement of the mobile node which executes communication by utilizing the IPv4, in accordance with the Mobile IPv4 procedures. Similarly, in the Mobile IPv6, messages are exchanged between a mobile node moving between the networks and a mobile agent (hereinafter called the "IPv6 mobile agent") for assisting the movement of the mobile node that executes communication by utilizing the IPv6, in accordance with the Mobile IPv6 procedures.
Let's consider the case where the IPv4/v6 mobile node supporting both of Mobile IPv4 and Mobile IPv6 inside the IPv4/v6 network moves to another IPv4/v6 network. Because the foreign IPv4/v6 network can execute communication by utilizing both of IPv4 and IPv6, the IPv4/v6 mobile node can exchange the messages with both of the IPv4 mobile agent and the IPv6 mobile agent on the network in accordance with the procedures of the Mobile IPv4 and the Mobile IPv6. Therefore, the movement of this IPv4/v6 mobile node between the networks is supported by both of the Mobile IPv4 and the Mobile IPv6. In consequence, the IPv4/v6 mobile node that has moved to the foreign network can successively execute communication without changing setting of the IP address and without cutting off the network connection that has been established already with other IPv4 node or the IPv6 node before its movement by utilizing the IPv4 or IPv6. It can also execute afresh communication with other node by utilizing the IPv4 and the IPv6.
Next, let's consider the case where the IPv4/v6 mobile node moves from the IPv4/v6 network to the IPv4 network which can execute communication in accordance with only the IPv4 and supports the Mobile IPv4. In this case, since communication by utilizing the IPv4 is possible between the IPv4/v6 mobile node and the IPv4 mobile agent, the assistance of movement of this mobile node between the networks by the Mobile IPv4 can be made. Therefore, the IPv4/v6 mobile node can execute communication successively after the movement without cutting off the network connection that has been previously established already with other IPv4 node by utilizing the IPv4. The mobile node can also execute communication afresh by utilizing the IPv4.
However, the mobile node cannot execute communication by utilizing the IPv6 on the IPv4 network and consequently, the exchange of the message on the IPv4 network in accordance with the Mobile IPv6 procedure becomes impossible between the IPv4/v6 mobile node and the IPv6 mobile agent. In other words, the assistance of the movement of the mobile node to the IPv4 network in accordance with the Mobile IPv6 becomes impossible and the IPv4/v6 mobile node that has moved to the IPv4 network cannot maintain the network that has been established already with other IPv6 node by utilizing the IPv6 before the movement and consequently, cannot execute communication. This mobile node cannot execute afresh communication with other node on the IPv4 network by utilizing the IPv6, either.
Similarly, let's consider the case where the IPv4/v6 mobile node moves from the IPv4/v6 network to the IPv6 network which can execute communication by utilizing only the IPv6 and supports the Mobile IPv6. In this case, too, the IPv4/v6 mobile node cannot execute communication by utilizing the IPv4 on the IPv6 network. In consequence, the exchange of the message in accordance with the Mobile IPv4 procedure is not possible on the IPv6 network between the IPv4/v6 mobile agent and the IPv4 mobile agent, so that the assistance of the movement of this mobile node to the IPv6 network in accordance with the Mobile IPv4 becomes impossible on the IPv6 network.